The ocean covers more than two-thirds of our planet, and there’s so much of it left unexplored. How are we humans supposed to blend in to uncover all of its secrets, when our observation tools are hooked to clunky vehicles with fish-scaring propellers and jets?

A team at Massachusetts Institute of Technology has unveiled their own solution—an ultrasound-controlled, soft robotic fish. It’s not the only fish robot out there, but it could be the first that can swim in three dimensions, untethered, in the open ocean. Such a robot has the potential to transform the way biologists study the ocean.

“The fish robot can become a platform for biologists to study marine life and use it for controlled studies,” study first author Robert Katzschmann told Gizmodo. “Not only in a tank, but in natural habitats like coral reefs and other environments that are of interest.”

This robo-fish is around the size of a salmon. It has a stretchy polymer tail that undulates via a hydraulic pump to control its movement. Rotating fake fins allow it to change depth. A human operator controls the fish with a remote control—which is made from a waterproofed Super Nintendo controller, study author Joseph DelPreto told Gizmodo.

The Nintendo controller speaks to the fish by sending vibrations through the ocean at frequencies higher than humans can hear. These pulses are essentially commands translated into binary code (or perhaps Morse code), which the robo-fish can read despite the background vibrations of the ocean. The researchers tested their creation out in the Pacific Ocean, at depths from zero to 18 metres (59 feet), according to the study published Wednesday in Science Robotics.

Preliminary results show that other fish seem mostly unperturbed by the robo-fish. I’m not sure what would happen if a shark tried to eat it, though.

There’s more work to be done. The researchers are currently limited by the fish’s speed, depth, and operational time, which is around 40 minutes.

But perhaps one day, combined with sensors and camera, the bot’s motion could be pre-programmed with commands like “follow that other fish” or “explore that reef.” The researchers dream of deploying a whole school of these fish, and have them receive their commands remotely via an ultrasound-emitting buoy. Perhaps with added solar power, the fish could simply resurface to charge.

The possibilities are endless. “In the aftermath of publishing the paper I’m sure biologists will tell us more use cases,” said Katzschmann. “There’s lots we have never seen.” [Science Robotics]